Cruz was expelled from the high school for unspecified disciplinary reasons, said officials, who provided different spellings of Cruz's first name throughout the day.

Officials are examining Cruz's digital profile, which contained what Israel described as "very, very disturbing" content.

Arrested without incident

Cruz was taken into custody without incident in nearby Coral Springs after the shootings, according to Israel.

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The suspect has been talking to investigators, according to a law enforcement source.

Heavily armed

Police said Cruz was armed with multiple magazines and at least one AR-15 style rifle.

Law enforcement sources told CNN the Bureau of Alcohol, Tobacco, Firearms and Explosives is tracing the.223 caliber, AR-15 style firearm used in the shootings.

Suspect sought higher death toll

Investigators believe the suspect pulled the school's fire alarm to draw people out and get a higher death toll, according to a law enforcement source.

There had been a fire drill at the school earlier in the day, leading some to believe at first that the afternoon incident was another drill, a student told CNN affiliate WSVN. "Everyone just started freaking out."

"But then word started going around that it was shots and not just, like, something else, everyone just started running towards the canal," the student said.